The present invention relates to a diversity wireless device used for wireless communications, and more particularly to a diversity wireless device suitable for use in a wireless terminal unit for a wireless local area network (LAN), such as a wireless PC card.
The antenna diversity used for wireless communications and the like is an effective means of eliminating influence of fading from received signals.
Generally, xe2x80x9cfadingxe2x80x9d is a phenomenon in which variation of medium on a radio wave propagation path or the movement of mobile communication equipment through areas with different field intensities changes the strength of received signals rapidly. In addition, xe2x80x9cdiversityxe2x80x9d means ensuring highly-reliable communications by preparing a plurality of antennas and synthesizing or switching two or more signals received at a reception side in a suitable manner when fading deteriorates the receiving condition.
General methods of providing diversity used for wireless communications and the like are as follows. That is, signals are separately received by two or more receiving systems that have a low degree of correlation therebetween and the received signals are synthesized or automatically switched before or after demodulation and then used. Typical examples of such methods include space diversity and polarization diversity.
The space diversity utilizes the fact that the variations caused by the fading at points separated from each other in the vicinity of a receiving point are independent of each other. Generally, two or more antennas are arranged so as to be spatially separated from each other and receive signals separately. Then, the signals are used after being synthesized or switched. The polarization diversity is a method of separately receiving signals using polarized wave receiving antennas that are arranged 90xc2x0 different from each other. Either method can provide the greater diversity gain when the antennas have the lower degree of correlation therebetween.
FIG. 15 shows a structure of a conventional diversity wireless device (for example, disclosed in Japanese Patent Application Non-Examined Publication No. H07-131229).
In FIG. 15, substrate 3910 has antennas 3930 and 3940 mounted thereon. Formed on substrate 3910 is ground plane 3920. Antenna 3930 has feed terminal 3931 and ground terminal 3932 that also serves to support the antenna. Similarly, antenna 3940 has feed terminal 3941 and ground terminal 3942 that also serves to support the antenna. In addition, mounted on substrate 3910 is radio frequency (RF) circuit 3950. RF circuit 3950 performs such operations as switching transmission/reception antennas, feeding power into the antennas, and processing received signals. The ground of RF circuit 3950 connects to ground plane 3920. In this structure, antennas 3930 and 3940 are so-called inverted F-type antennas, in which ground plane 3920 also affects the antenna characteristics.
In recent years, there has been a strong request for downsizing of wireless devices. The downsizing have necessitated the smaller space assigned to antennas. Therefore, only insufficient space can be provided between antennas. This makes a higher degree of correlation between the antennas connected to a common ground, thus resulting in reduction in the diversity gains.
In addition, in recent years, with the progress of networking in offices and at home, a plurality of personal computers (hereinafter referred to as PC) is connected via Internet or other networks and LANs are built. On the other hand, networking using wireless devices has been drawing attention because it does not have the problems of troublesome rewiring at a layout change and difficulty in new wiring. Especially, because the Institute of Electrical and Electronics Engineers (IEEE) standardized a transmission speed of 11 Mbps equivalent to that attained with wire devices, the introduction of wireless LANs has been promoted at a cheaper price than ever. An adapter for a wireless LAN is available as a wireless PC card, in which the space its wireless part can occupy is limited. Therefore, the wireless part including its antenna part is structured to have its own features.
Known conventional wireless PC cards include the invention disclosed in Japanese Patent Publication No. 3004533 and the utility model disclosed in Japanese Utility Model Publication No. 3041690, both of which are built with inverted F-type antennas.
FIG. 14A is a perspective view illustrating an appearance of a wireless PC card as a conventional portable wireless terminal unit. FIG. 14B is a perspective view illustrating the antenna arrangement part of the PC card. FIG. 14C is a cross-sectional view of the card including its enclosure taken on line 14Cxe2x80x9414C of FIG. 14B.
As shown in FIGS. 14A and 14C, the wireless PC card has extended part 3620 covered with frame 3590, top sheet metal cover 3600, and bottom sheet metal cover 3610. This extended part 3620 includes a plurality of antenna elements therein. In other words, as shown in FIG. 14B, extended part 3620 has conductor section 3510 serving as a first antenna element, conductor section 3520 serving as a second antenna element and ground plane 3580 on circuit board 3570. Conductor section 3510 has feed terminal 3530 and ground terminal 3540 bending at and protruding from the edges of the conductor section. With its terminal 3540 grounded to ground plane 3580 on substrate 3570, the conductor section serves as an inverted F-type antenna. Similarly, conductor section 3520 has feed terminal 3550 and ground terminal 3560 bending at and protruding from the edges of the conductor section. With its terminal 3560 grounded to ground plane 3580, the conductor section serves as an inverted F-type antenna.
Two antenna elements are used for the following reasons: antenna element 3510 and antenna element 3520 provide diversity; and one with better characteristics is selected from these antenna elements by switching them using a switch (not shown) when the variations in intensity of received waves are caused by such influences as fading.
In general, the size of the extended part of a wireless PC card used as a wireless LAN card is determined by the standard of PC cardsxe2x80x9454 mm in width, 40 mm in length and 10.5 mm in height. Characterized in that they have high performance and can be downsized, the inverted F-type antennas are often used for a wireless PC card.
Now, the characteristics of the inverted F-type antennas are the better at the greater distance between substrate 3570 and conductor sections 3510 and 3520 (the distance shown at xe2x80x9chxe2x80x9d in FIG. 14C). Therefore, it is important to make the distance xe2x80x9chxe2x80x9d longer. However, when the distance xe2x80x9chxe2x80x9d is determined to the limit of its standard, extended part 3620 is too large as shown in FIG. 14A, thus imposing some limitations on the design of its shape.
The present invention addresses the above-mentioned problem and aims to provide a diversity wireless device and a wireless terminal unit that can be downsized without reduction in their diversity gains.
A diversity wireless device in accordance with the present invention is structured as a diversity wireless device providing diversity using a plurality of antennas. The device has antennas that are grounded (grounded antennas) and antennas that are not grounded (ungrounded antennas).
Another diversity wireless device in accordance with the present invention is structured as a diversity wireless device providing diversity using a plurality of ungrounded antennas. The device is structured so that a ground is provided in the vicinity of at least one of the ungrounded antennas and the ungrounded antenna is coupled to the ground via high-frequency waves.
Still another diversity wireless device in accordance with the present invention is structured as a diversity wireless device providing diversity using a plurality of antennas. The device is structured so that it has at least one ungrounded antenna and a ground partly surrounding the ungrounded antenna and that the ungrounded antenna and the ground are coupled to each other via high-frequency waves.
These structures allow downsizing of the devices without reducing their diversity gains.
A wireless terminal unit in accordance with the present invention is structured as a wireless terminal unit having an antenna element. The terminal unit is structured so that the antenna element includes:
(a) a substrate;
(b) a first conductor section substantially parallel to the substrate; and
(c) a second conductor section successively formed from the first conductor section and angularly arranged relative to said substrate.
This structure allows a change in the height of the antenna element part, thus offering an advantage of reducing limitations on the design of the antenna part.